FMD55 1999 Page 4
The lead from the antenna to the receiver must be a non-
dissapative well shielded coaxial cable with the same impedance
as the receiver input. These are usually laid parallel to other
(disturbing) cables and near other electrical devices. A badly
shielded cable picks up local interference and transmits them to the
receiver.
The receiver itself should be connected at the shortest possible
distance to a grounding sponge.
Alternatively an active antenna can be used. The input resistor in the
amplifier of an active antenna is very high, therefore it requires a
very short whip. The output resistor of the amplifier is 50: throughout
the whole of the specified frequency range, so that a corresponding
coaxial cable also with 50: which transmits the signal from the
antenna without further loss of adaptation. The difficulty in the
realisation of a good active antenna is that the integrated amplifier
and the impedance transformer are as linear as possible and not
over-modulated by strong signals from nearby transmitting stations
creating self generated interference to the receiver. This is normally
only possible with powerful amplifiers with equally high voltage use
demands finding a good solution between highest possible linearity
and the least amount of draw of current.
Because of the small dimensions, it is easier to find a place for
mounting an active antenna away from disturbing influences. The
lead to the receiver through the shielded coaxial cable is
uncritical. The use of a high quality active antenna will give an
optimum reception.
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